Over the last thirty years, a technique of packaging articles has been used in which a heat-shrink film implemented in the form of a sleeve is engaged on the article(s) for packaging, and is then heat-shrunk thereon. In general, the sleeve is obtained from a film that is folded in half and looped by bonding together its two corresponding end zones.
To illustrate this technological background, reference may be made to numerous patent documents in the name of the Applicant, and in particular to documents EP-0 879 189 B1, EP-1 082 256 B1, EP-1 294 614 B1, and EP-1 513 739 B1.
Reference may also be made to document EP-1 790 578 A1 that describes a rotatable sleeve of heat-shrink plastics material presenting one or two windows for viewing inscriptions that are on the outside surface of the wrapped container.
Finally, the technological background is illustrated by document DE-883 700 C that shows a label adhesively bonded via its vertical edges, and leaving a central portion that is detachable.
In several domains, for example the food, pharmaceutical, or medical domains, it is necessary to protect substances contained in a container from light radiation, in particular ultraviolet (UV) radiation, with this applying both to the visible spectrum and to the invisible spectrum, i.e. for wavelengths up to 500 nanometers (nm). By way of example, in the food domain, mention may be made of milk products where a light barrier is necessary in order to preserve the color, the vitamin components, and the organoleptic properties of the products concerned. In the pharmaceutical or medical domains, mention may also be made of packaging substances for perfusion, transfusion, or cancer treatments. Finally, transfusion substances that are mixed together extemporaneously, may also need to be protected from light radiation.
In these various domains, it can be necessary to verify the level of substance within the container, or to verify the presence of substance therein, or indeed to verify the mixing of a plurality of substances, when it is desired to verify that they are indeed miscible.
Unfortunately, specialists are then confronted with a difficulty, since there is contradiction between providing overall protection against light radiation over the entire side surface of the container, and allowing the presence of the substance or the level of the substance in the container to be verified by eye. In this context, it should be observed that a line of microperforations defining a detachable window would suffice to negate the light-barrier property, and is therefore not suitable.